Quietive is a noun that refers to something that has a soothing effect.

The root word of quietive is quiet, from a Latin word which, of course, means quiet. The suffix I-V-E refers to ‘that which performs toward.’ In this case, a quietive performs toward a ‘quieting’ or soothing of a person’s temperament.

Even after taking the quietive the doctor prescribed, I couldn’t help but feel a little nerved wracked. The soothing effect took much longer for me to feel.